BFRP加固混凝土界面粘结强度影响因素研究

为了探究BFRP加固混凝土界面粘结强度的影响因素,文中通过作者参与的BFRP加固混凝土的双剪试验,根据试验过程、试验结果以及分析,归纳出BFRP-混凝土界面粘结强度的主要影响因素有混凝土强度等级、粘结长度、胶层厚度以及粘结宽度。文中针对这四种影响因素进行综合分析得出以下结论,混凝土强度等级,界面粘结强度随混凝土强度等级提高而增大;粘结长度,有效粘结长度范围内,界面粘结强度随粘结长度增加而增大;胶层厚度,界面粘结强度随胶层厚度增加而增大。粘结宽度,界面粘结强度随粘结宽度的增加而减小。其中,混凝土强度等级和粘结长度是影响界面粘结强度的主要因素。     

BFRP加固混凝土界面粘结疲劳试验结果及分析

近年来玄武岩增强材料,即BFRP,得到了广泛的推广。由于在损伤部位粘贴BFRP加固材料从而达到修复结构损伤的方法简单且施工简便,因此,成为加固和修复钢筋混凝土结构的主要方法。本文对BFRP-混凝土界面粘结疲劳试验的过程及结果进行归纳,分析疲劳循环次数下界面的应变分布规律,总结出影响BFRP-混凝土界面粘结疲劳强度的影响因素有BFRP粘结长度、胶层厚度和混凝土强度等级。     

铝合金板混凝土界面的粘结滑移性能及其本构关系

铝合金板具有轻质高强、耐腐蚀性和延展性好等优点,是复杂恶劣环境中加固混凝土结构的理想材料。基于双剪试验进行铝合金混凝土界面粘结滑移性能研究,完成了45个构件的双面纯剪试验,得到了其破坏形态、荷载应变关系曲线、粘结界面剪应力分布曲线、荷载滑移关系曲线以及界面极限承载力,分析了不同的混凝土强度等级、铝合金板表面粗糙度、铝合金板粘结长度和粘结宽度条件下界面粘结滑移性能的演化规律。研究表明:加载过程中,界面应力从加载端向自由端逐步传递,且随着混凝土强度等级、铝合金板的粘结长度和宽度的增加,试件的剥离承载力也有所提高。但铝合金的粘结长度存在一个有效粘结长度值,超过该值试件的剥离承载力将不再增加,同时,铝合金表面粗糙度对试件剥离承载力的提高没有实质影响。通过测量铝合金板的应变得到了不同参数条件下铝合金板混凝土粘结滑移本构曲线,结果表明:铝合金板混凝土粘结滑移本构曲线存在明显的界面软化特征和非线性行为。     

铝合金板与混凝土的粘结性能

铝合金材料具有强度高、变形性能好、耐腐蚀等优点,是沿海侵蚀环境中钢筋混凝土结构加固工程的理想材料;而铝合金板与混凝土的粘结性能是铝合金板加固钢筋混凝土梁能否协同工作的关键问题。基于此,对铝合金板与混凝土的粘结性能进行试验和理论研究。考虑混凝土强度、铝合金板宽度和厚度、粘贴长度及界面处理等因素对铝合金板和混凝土块体粘结性能的影响,设计了一套试件固定装置,采用万能试验机对105个铝合金板与混凝土棱柱体的粘贴试件进行了面内单剪试验。根据试验结果,结合理论分析,得到了铝合金板和混凝土连接的粘结破坏典型特征、剪应力分布曲线和粘结滑移曲线。研究表明,试件存在两种破坏形式:界面剥离破坏和混凝土层剥离破坏。界面处理对粘结性能有重要的影响,粘贴界面没有进行糙化处理的试件发生了界面剥离破坏,其他试件发生了混凝土层剥离破坏;随着混凝土强度的提高、铝合金板宽度和厚度的变小,粘结性能提高;存在一个有效粘贴长度,当粘贴长度大于有效粘贴长度后,增大粘贴长度并不能提高连接的极限荷载。     

碳纤维片材与混凝土有效粘结长度的试验研究

有效粘结长度是碳纤维增强片材(Carbon Fiber Reinforced Polymer,CFRP)与混凝土的临界粘结长度,超过这个临界粘结长度,CFRP与混凝土界面承载能力就不会增加.通过粘贴CFRP片材加固切口混凝土梁三点弯曲试验,研究CFRP片材粘结厚度、粘结宽度以及混凝土强度等级对CFRP与混凝土之间有效粘结长度的影响.结果表明:随着CFRP粘结厚度的增加,CFRP与混凝土之间的有效粘结长度相应提高,但是,有效粘结长度与CFRP粘结厚度并非线性关系;CFRP粘结宽度、混凝土强度等级等对有效粘结长度影响不显著.基于对试验结果的分析,提出了CFRP片材与混凝土有效粘结长度计算公式,计算结果与试验结果符合较好.     

疲劳荷载下CFRP布加固损伤钢筋混凝土梁粘结性能试验分析

在加固工程中,CFRP布-混凝土界面的有效粘结是决定加固效果的关键因素。针对四根已产生疲劳损伤的足尺钢筋混凝土梁进行CFRP布加固,考虑原钢筋混凝土梁损伤程度和疲劳幅值影响,对CFRP布加固损伤钢筋混凝土梁界面的粘结性能进行疲劳试验研究,探讨CFRP布-混凝土界面在疲劳荷载作用下的粘结应力分布以及加固后试验梁的疲劳粘结性能。结果表明:试验梁初始损伤程度和疲劳幅值越大,CFRP布-混凝土界面的粘结性能越差,疲劳寿命越小;当疲劳幅值超过0. 6时,加固梁的疲劳寿命急剧下降,发生脆性疲劳粘结破坏。     

聚合物砂浆与混凝土抗拉粘结性能研究

高强不锈钢绞线网-渗透性聚合物砂浆加固技术是近年来兴起的新型加固工艺。对该加固技术的研究表明:加固层发生剥离破坏是其主要破坏方式之一,如何保证加固层与混凝土界面的粘结性能是加固成败的关键。通过243个测点的正拉粘结强度试验,分析聚合物砂浆与混凝土界面粘结抗拉性能,阐述混凝土强度、界面粗糙度、龄期、修补方位对正拉粘结强度的影响,最后提出正拉粘结强度的计算模型。     

FRP-混凝土界面粘结性能有限元方法研究

分析FRP-混凝土界面的粘结性能, 是研究FRP外贴加固钢筋混凝土结构的基础问题。本文根据已有的面内剪切试验研究结果, 采用大型通用有限元程序MSC.Marc建立有限元模型并导入裂面剪力模型子程序, 进行了非线性计算分析。引入了“裂缝带模型”、“界面粘结承载力”、“有效锚固长度”等概念, 对混凝土单元开裂软化模量以及裂面剪力模型进行了优选。得到了FRP应变分布规律和界面粘结应力分布规律, 提出了全新的“粘结屈服平台”概念, 建议相关的界面性能非线性有限元分析采用本文的方法。     

混凝土和聚合砂浆粘结界面的剪切性能试验研究

混凝土和聚合砂浆粘结界面的剪切性能试验结果,对于估算混凝土结构的修补和加固面积与长度具有重要的参考价值。介绍了对3组聚合砂浆与混凝土粘结试件进行的剪切试验,并对测试结果进行了讨论,得出砂浆和混凝土粘结剪切强度以及粘结剪切性能的一般规律。     

CFRP片材加固RC梁界面粘结破坏机理分析

CFRP加固混凝土结构中,CFRP与混凝土之间的界面粘结和剥离问题显得尤为突出,通过对此具有代表性研究成果的总结,简要介绍了几种CFRP加固混凝土结构的界面粘结破坏模式及其破坏机理。     

盐腐蚀环境下内嵌FRP筋加固混凝土界面黏结性能试验研究

为了研究盐腐蚀环境下内嵌FRP筋加固混凝土界面的黏结性能,对27个内嵌FRP筋加固混凝土试件进行盐腐蚀后的单端拉拔试验,分析试件的受力过程和破坏模式,研究内嵌FRP筋黏结长度、腐蚀时间和FRP筋类型对界面黏结性能的影响。结果表明：盐腐蚀的试件破坏模式分为结构胶劈裂、FRP筋拉断和结构胶劈裂且FRP筋弯折等3种,且以结构胶劈裂破坏为主。盐腐蚀环境下内嵌FRP筋混凝土试件的黏结应力与黏结长度、破坏模式与腐蚀时间有关。盐腐蚀环境会影响混凝土、黏结材料及FRP筋的力学性能,加剧黏结界面失效破坏。腐蚀时间为30 d和90 d的内嵌BFRP筋加固混凝土试件的耐盐腐蚀能力高于内嵌GFRP筋加固混凝土试件的,腐蚀时间为60 d的内嵌GFRP筋加固混凝土试件的耐盐腐蚀能力优于内嵌BFRP筋试件的。根据试验数据拟合了盐腐蚀环境下内嵌FRP筋加固混凝土界面黏结-滑移本构关系,其拟合优度达到0.988 0。     

Strain monitoring of RC members strengthened with smart NSM FRP bars

Fiber-reinforced polymer (FRP) bars can be used as internal reinforcement for new reinforced concrete (RC) structures and as near-surface mounted (NSM) reinforcement for the strengthening of RC structures. The NSM method is an emerging strengthening technique for RC structures, where FRP bars are embedded into grooves cut in the cover of RC members. In both cases, strain monitoring of the FRP bars is desirable either for the investigation of the structural behavior or for the long-term health monitoring of the structure. This paper presents a study in which fiber-optic sensors were embedded into glass FRP (GFRP) bars to produce smart GFRP bars for NSM applications. The manufacturing process of the smart FRP bars is illustrated and their performance in tensile, bond and beam flexural tests is examined to assess the effectiveness of these smart FRP bars for achieving the dual purpose of structural strengthening and strain monitoring. On the basis of the test results, the advantages and limitations of fiber-optic sensors compared to electrical strain gages in the strain monitoring of NSM FRP bars are discussed. The bond and beam test results also confirm the effectiveness of the NSM method for the strengthening of RC structures.     

表层嵌贴预应力CFRP板条加固钢筋混凝土梁的应力传递行为

表层嵌贴预应力FRP板条加固钢筋混凝土结构技术可充分发挥FRP材料强度,且不需设置永久锚具,具有较大的潜力。以试验得到的嵌贴FRP混凝土粘结滑移关系为基础,建立了嵌贴预应力CFRP板条与混凝土的粘结应力微分方程,并根据边界条件推导了方程的解析解,得到了嵌贴预应力CFRP板条放张后界面粘结应力、CFRP拉伸应力的分析模型。与试验结果的比较表明,该模型得出的界面粘结应力及CFRP拉伸应力与试验结果吻合较好。在此基础上,考虑放张后CFRP混凝土界面不出现剥离的条件,分析了粘结界面能抵抗的最大容许预应力。     

Modeling of debonding failure for RC beams strengthened in shear with NSM FRP reinforcement

The shear capacity of reinforced concrete members can be successfully increased using near-surface mounted (NSM) fiber-reinforced polymer (FRP) reinforcement. Tests conducted thus far have shown that failure is often controlled by diagonal tension associated to debonding between the NSM reinforcement and the concrete substrate. In absence of steel stirrups and/or when the spacing of the NSM reinforcement is large, debonding involves separately each of the bars crossed by the critical shear crack. In order for shear strengthening of beams with NSM reinforcement to be safely designed, an analytical model able to encompass the failure mode mentioned above must be developed. This paper presents two possible approaches, a simplified and a more sophisticated one, to predict the FRP contribution to the shear capacity. In the first approach, suitable for immediate design use, an ideally plastic bond–slip behavior of the NSM reinforcement is assumed, which implies a complete redistribution of the bond stresses along the reinforcement at ultimate. The second approach, implemented numerically, accounts for detailed bond–slip modeling of the NSM reinforcement, considering different types of local bond–slip laws calibrated during previous experimental investigations. It also takes advantage of an approach developed by previous researchers to evaluate the interaction between the contributions of steel stirrups and FRP reinforcement to the shear capacity. The paper illustrates the two models and compares their predictions, with the ultimate goal to evaluate whether the first simple model can be used expecting the same safety in predictions of the second model.     

FRP材料加固混凝土结构应用的新领域--嵌入式(NSM)加固法

嵌入式 (NSM)加固法是FRP材料加固混凝土结构的一种新的应用形式 ,较外贴加固在某些方面具有明显优势。目前该技术在国内的研究应用尚属空白 ,对在该领域已有的国外文献从材料、试验研究、粘结性能和设计方法等几个方面进行了总结 ,可为国内今后开展相关的研究和应用提供借鉴和参考。     

Three dimensional mechanical model for simulating the NSM FRP strips shear strength contribution to RC beams

Shear strengthening of Reinforced Concrete (RC) beams by means of Near Surface Mounted (NSM) Fiber Reinforced Polymer (FRP) strips is an emerging technique for structural rehabilitation that is gaining increasing interest in the FRP community, mainly because of some advantages it provides with respect to the better consolidated technique of the Externally Bonded Reinforcement (EBR). Those advantages mainly encompass a better exploitation of material and a higher protection against vandalism, along with a relative faster applicability. Yet, the behavior of such NSM FRP strips is extremely complex, as can be gathered by experimental evidence, due to the complex geometry, the nonlinear mechanical properties of bond, and the scatter affecting the concrete tensile properties, along with their nonlinearity. In an attempt to provide valuable contribution to a better understanding of their behavior, a three dimensional mechanical model for simulating the shear strength contribution provided by a system of NSM FRPs to a RC beam throughout the loading process is herein presented along with the main findings. It correctly interprets the experimental evidence, taking into account complex phenomena such as the interaction between bond transferred force and concrete fracture, along with the interaction between adjacent strips.     

Modelling of the bond–slip behavior in FRP reinforced masonry

The strengthening of out-of-plane loaded unreinforced masonry (URM) walls strengthened with near-surface mounted (NSM) FRP strips has proven to be an innovative and cost effective strengthening technique. Since the performance of FRP-strengthened URM walls is often controlled by the behavior of the interface between the FRP and masonry, it is very important to model the bond–slip relationship accurately. In this paper, the bond–slip behavior of the FRP-to-masonry interface in a pull test was simulated by solid continuum elements where detailed information of the interface could be modelled directly. The masonry prism in the pull test was modelled using a previously derived homogenized model. For comparisons of computational efficiency, a continuum model, in which the mortar and masonry brick units are discritized individually, and the commonly used smeared-crack model were also employed to model the masonry prism in the pull test. A thin layer of interface elements was used to simulate the behavior of the FRP-to-masonry interfaces in each model. The accuracy and efficiency of the homogenized model together with the interface elements was validated by experimental data from (a) uniaxial pull tests of a NSM strip bonded to a masonry prism and (b) an out-of-plane loaded full-scale masonry wall strengthened with NSM CFRP strips running in the vertical direction. The simulated results using the homogenized model were found to agree well with test data from both sets of tests.     

Evaluation of the transfer length of prestressed near surface mounted CFRP rods in concrete

The transfer length of a prestressed near surface mounted (NSM) fiber reinforced polymer (FRP) rod is the distance over which the rod must be bonded to the epoxy to develop the prestressing force in the rod. The transfer length is intended to provide bond integrity for the strengthened concrete member. This paper presents experimental results and an empirical equation to estimate the transfer length of prestressed NSM Carbon FRP (CFRP) rod in concrete beams. Twenty-two reinforced concrete specimens were strengthened with NSM CFRP rods. Two types of CFRP rods were used: spirally wound and sand blasted rods. Four prestressing levels were used: 40%, 45%, 50% and 60% of the tensile strength of the CFRP rod. The strain behavior in the CFRP rod was monitored by gauges mounted on the CFRP rod along the length of the beam. The test results showed that the transfer length of the prestressed NSM CFRP rod was about 35 times the diameter of the CFRP rod. The maximum bond stress of the CFRP rod in epoxy was found to range from 11 to 16 MPa for the sand blasted rods and from 12 to 23 MPa for the spirally wound rods. An empirical expression based on curve fitting of the measured data was proposed to predict the prestressing stress in the CFRP rod along the length of the beam.     

Construction tolerances and design parameters for NSM FRP reinforcement in concrete beams

Aging infrastructure worldwide has made rapid means of repair and retrofitting a growing necessity. Fiber reinforced polymers (FRP) can provide a cost-effective and accelerated repair technique with near surface mounting (NSM) of pre-cured bars or strips in a bed of epoxy placed in pre-cut grooves. The performance of NSM FRP reinforcement depends on both geometric and mechanical properties of the system. Within the scope of this study, an experimental program was carried out to identify the effects of groove size tolerance on NSM FRP systems. Test results showed that the groove size tolerance up to ±22% does not affect the overall performance of such systems. The findings were also verified with a finite element model, which was then extended to study the effects of other geometric and physical parameters. Finally, a comprehensive database of test results available in the literature was compiled, and a comparative study was conducted on the geometric and material properties of the NSM FRP systems.     

Bond behaviour of FRP-to-clay brick masonry joints

The out-of-plane bending and in-plane shear response of unreinforced modern clay brick masonry walls retrofitted with fibre-reinforced polymer (FRP) strips is often governed by debonding failure mechanisms. Hence, it is necessary to quantify the fundamental interface bond–slip model, which describes the debonding behaviour of the FRP-to-masonry interface. This paper presents the results of a series of 29 pull tests investigating the use of externally bonded (EB) and near surface mounted (NSM) retrofitting techniques. Test variables included: surface preparation; geometric properties; location of FRP (relative to perpend joints and cores); bonding agent of bed joints (mortar and quick drying paste); bonding method for glass fibre sheets (plate bonding and dry lay-up); and FRP material. A discussion of the test results and preliminary practical recommendations are also provided. A model used to predict the intermediate crack debonding resistance was verified against the test data. The model is generic in that it is applicable to both the EB and NSM retrofitting techniques. This generic model was shown to give very good ultimate strength predictions for the series of 29 pull tests conducted as part of this research.